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Old 11-02-2011, 01:19 PM   #1
jsd
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timing chain broke ... damage?

this is my first time posting but hopefully people will still help. I just finished replacing the head gasket on my 330i. I started the engine and it ran, I then stopped the car to check the coolant and oil levels before starting again. when I went to start the engine again I heard a pop and it would not start. unfortunatly I turned the engine over many more times to check for fuel and spark. When I took the valve cover off I found that the secondary timing chain had broken (the chain between the camshaft sprockets). It destroyed my tensioner too. The thing that most surprised me was all of the coolant in the head area. It poored out of my vanos unit when I took it off (I assume I will have to rebuild this too now). I had my head surfaced and checked for cracks so I know the head was in good shape.

My question is what could cause these events to transpire. I found little to no information on these problems so I assume they are rare. What could I have done wrong? If the valves and pistons are ok what can I do to avoid these problems again. (I will try to get the head off again tonight) Thanks for any help.
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Old 11-02-2011, 01:30 PM   #2
new//M3fan
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Did you time the VANOS relative to the camshafts and TDC?
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Old 11-02-2011, 01:39 PM   #3
jsd
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I didn't know there was a way to time the vanos. The diy I was following only mentioned setting the camshafts and crankshaft at tdc together. I turned the engone over a few times before putting the vanos unit back on to make sure that the engine was timed right. All the markers on the pieces at the end of the camshafts lined up the same way as the pictures I took when dissasembling the engine. assuming the head and engine can be salvaged how would I go about timing the vanos or are there diy's in place for that already? thanks
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Old 11-02-2011, 01:49 PM   #4
new//M3fan
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You need this tool

http://www.baumtools.com/pdf/bmw_cam-timing.pdf\

And install the VANOS gear into the camshaft the right way.
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Last edited by new//M3fan; 11-02-2011 at 01:50 PM.
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Old 11-02-2011, 01:56 PM   #5
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I used all of those and the camshaft locking fixture. the engine ran for a few seconds before I turned it off, so I'm inclined to believe that the timing was set up properly before the timing chain broke. the alternative theory that I have is that at the low speeds when I hand cranked the engine, the valve to piston interference was not pronounced enough for me to feel it. So that when the engine turned at speed the timing chain snapped as a result of a valve and piston coming in contact
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Old 11-02-2011, 01:56 PM   #6
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I've been hanging here a while and as you suspect I've never heard of anyone with that issue. Some thoughts :

The timing chain broke so it's possible that thing is timed incorrectly. If the slave camshaft valves make contact with the piston during the upstroke, the master camshaft (the one driven by the crank) will continue turning and proceed to break the small chain.

Coolant in the head area is alarming. I haven't been inside the M54 in a while but I don't remember the VANOS assembly being directly cooled, hence the coolant (if it was indeed that) is coming from a cracked head.

Some here have successfully timed their M54s, although I do remember that involves special tools. As far as procedure, even car "vets" have confessed messing things up with the M54. Experts like jbeurotech will have a better (real world) understanding. Hopefully he's watching and will give you an idea.
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Old 11-02-2011, 02:02 PM   #7
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You replaced the head gasket and inspected the head so I'm assuming the motor had previously overheated? Were you able to achieve proper torque when tightening down the head? I'm wondering if there wasn't damage to the block and if the head studs have now stripped out of the block allowing the head to lift (common problem when these engines overheat and why BMW recommends replacing the block). Running the car and then shutting it off obviously heated up the coolant and caused it to expand and pour out into places it shouldn't have been, one way or another. I wouldn't be surprised if you even hydrolocked the motor.

It's extremely rare for a timing chain to break though. Doesn't sound like you followed the proper procedures for timing the cams but worst case scenario there is you could have bent some valves. It's not obvious to me that there is any way this could have led to a broken timing chain and especially not the secondary (upper) chain. Only thing I could speculate is that the massive cooling leak flushed the cam bearings and caused one or both of the cams to seize in place. Perhaps it was just a random failure or perhaps it was related to the overheating but if everything is properly rebuilt (or the motor ends up being replaced), I wouldn't worry too much about future timing chain failures.
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Old 11-02-2011, 02:03 PM   #8
jasonbimmer
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VANOS has no coolant passage and it does not need cooling.
I dont believe you need to set timing when you do Vanos, but if you do timing chain then yes.
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Old 11-02-2011, 03:35 PM   #9
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thank you for the responses. It is possible that my engine overheated but an indicator light never came on for that and I never had low coolant. the block was able to hold down the proper torque for the bolts, I am sure of this because I forgot a step the first time and had to order a new set of bolts and they held torque again(at least I think, there was no familiar feeling of stripped threads. the engine had very little time to heat up the coolant as I only let it run for less than five seconds. the vanos unit is not connected to a coolant passage, the coolant/ oil mix was coming out of the oil pressurized passages (not supposed to be there). im with you guys though that the error was probably mine and not a random part going bad. my plan of action is to order a new head gasket, head bolts, a timing chain, and secondary chain tensioner. I will take the head back to the machine shop to have it inspected. and in the mean time flush the coolant and drain 7 quarts of unused full synthetic oil. when I put it back together I will focus even more on the timing even though I spent about 4 hrs the first time trying to make sure it was perfect. as this seems the most likely point of failure. I will post the results when I am done, but that time is indeterminate as I do not yet know what I will find when I open the engine back up.
Two other things I was wondering? are timing chains unidirectional like timing belts. and if the block is cracked how would I know, there is no leaking out of the block, I will check to see if any of the cylinders have coolant in them before unbolting the head.
Also if anyone has suggestions on clues to look for when disassembling the engine I am open to suggestions. thanks
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Old 11-02-2011, 03:52 PM   #10
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So what prompted you to change the head gasket in the first place? That isn't really considered routine maintenance.
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Old 11-02-2011, 04:13 PM   #11
jsd
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i went out to start my car one morning and it started idling really rough and white smoke was coming out of the tailpipe. it was a much different smell than when my oil separator went out. I had it towed to a shop and they said that I either had a cracked head or a blown head gasket. I'm wondering now with the coolant in the engine if I do have a cracked head and the machine shop I went to didnt test it properly. they came recommended from a mechanic that is a friend of mine.
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Old 11-02-2011, 04:16 PM   #12
jsd
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the specs I used were to follow the patterrn for the 14 bolts. 1st round torque to 30lb/ft, 2nd round 90 degrees, 3rd round 90 degrees. i felt the same resistance on each bolt. I had one bolt strip out while I was reinstalling the camshafts and that bolt felt very different.
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Old 11-08-2011, 03:20 AM   #13
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I can almost see what happened:

I replaced my head gasket myself too.

At the very least, you did not time the cams correctly. It requires a certain procedure. These are interference engines in that the valves will contact the pistons if not properly timed. I assume the incorrect timing caused valve interference enough to snap the chain. It might also have damaged the head to the point where a water canal was breached. Coolant coming from the Vanos is not right at all, as only oil goes in and out of there.

This is really the worst case scenario. The head must come off again, the head inspected and fixed, if even possible, which I question. Valves need to be replaced and re seated. Also inspect the Pistons for damage, though this would be obvious. You can also buy a used head. Some are out there for a few hundred. You will also need a new head gasket and bolts.

But you have to blame yourself for not knowing about the necessity for timing the cams. This is critical and I redid it like 5 times....

My engine runs like a champ now, smooth as butter.

Last edited by tommytoyz; 11-08-2011 at 03:24 AM.
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Old 11-02-2011, 04:11 PM   #14
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Were you able to get the head bolts tightened to spec? It seems usually the m54 when overheated also ruins the threads in the block could be the source of the coolant you are finding.
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